Holden may have some guilt about still being alive while Allie is dead. But the real problem is that Holden has not yet come to grips with Allie's death. He stopped growing emotionally when Allie died and is having difficult time moving on. He likes things that don't change ( like the natural history museum) and he wants to be a catcher in the rye in order to stop children from having to grow up. Facing adulthood means being able to move past events of one's childhood and deal with reality. Holden, however, is unable to do either. This is really Holden's problem throughout the novel. It's not that he feels so guilty about Allie's death; he just wishes Allie had not died at all. Whether this is normal or abnormal no one can say. All people deal with grief in different ways. The problem is that Holden hasn't faced the problem yet. Holden's parents just think he's crazy and Holden alienates so many people, he's able to hide his true feeling by being angry and anti-social.

Holden feels anger, self-denial, and yes, guilt, over Allie's death. He loved Allie and blames himself for his brother's death, as people generally do. That's why he punched out all the windows in the garage. That's why he slipped into such a heavy depression with mental anxiety. Is this abnormal? Hard to say. We have to keep in mind that JD Salinger is a WWII veteran who most likely had PTSD. That same mental anxiety and depression he had, he also wrote in for Holden (whether intentional or not). Holden's reaction to Allie's death is very plausible and therefore perhaps even normal.